Answers to Chapter 18 Review Questions
1. Some of the components of a compact fluorescent lightbulb (and the resources used to make one) are as follows:
- Steel (iron, carbon from coal plus some manganese, nickel, chromium, molybdenum)
- Plastic housing (petroleum)
- Glass coil (silica from sand, plus minor amounts of sodium, calcium, and magnesium)
- Copper conductors, lead solder, and basal contact
- Silica (sand), plastics (petroleum), ceramics (clay), aluminum, gold, copper, etc. in the electronics
- Mercury inside the tube (less than 5 mg)
2. Nickel deposits form within mafic and ultramafic igneous bodies because the original magma have relatively high nickel levels to begin with, while intermediate or felsic magma have low levels.
3. The “smoke” in a black smoker is composed of tiny crystals of sulphide minerals. If those include significant quantities of ore minerals like chalcopyrite (CuFeS2), sphalerite (ZnS), and galena (PbS), a VMS deposit could form during this process.
4. A porphyry deposit is situated in the rock around an igneous pluton that has intruded to a relatively high level in the crust (and hence is porphyritic), and they form at least in part from fluids released by the magma. Epigenetic gold deposits may be formed from the same or similar fluids, but are situated at a greater distance from the pluton/
5. Ferrous iron (Fe2+) is soluble in water with a low oxidation potential, and gets converted to insoluble ferric iron (Fe3+) when the water becomes oxidized. The opposite situation happens with uranium. Uranyl uranium (U6+) is soluble under oxidizing conditions, but when the water in which it is dissolved encounters reducing conditions the uranium is converted to the insoluble uranous ion (U4+).
6. It is common for the upper part of a kimberlite to be mined using an open pit (in this case around 500 m wide and up to 500 m deep), and for the lower part to be mined underground.
7. Pyrite (FeS2) is typically responsible for acid rock drainage around mine sites, and it is very common for pyrite to form within the rock at the same time that other metal sulphides (e.g., chalcopyrite) are forming.
8. Glaciofluvial gravels are typically relatively well sorted, and may include clasts ranging in size from coarse sand to pebbles. Till, on the other hand, tends to be poorly sorted and may have clasts ranging from clay to boulders. More processing would be needed to separate the required size ranges, and because till tends to be relatively hard and strong, this would require a lot of effort.
9. During the manufacture of CaO limestone is heated and CO2 is released to the atmosphere, adding to the greenhouse effect. The energy required for this process typically comes from fossil fuels (e.g., natural gas) and the combustion also releases CO2.
10. Some important evaporite minerals include halite (NaCl), sylvite (KCl), and gypsum (CaSO4.2H2O).
11. The 15 m of organic matter required to make 1.5 m of coal, is equivalent to 15,000 mm, and if the organic matter accumulates at 1 mm/y that would require 15,000 years. That organic matter would have to remain submerged in oxygen-poor water for at least that length of time.
12. Petroleum source rocks must have a significant component of organic matter, and then need to be buried to at least 2,500 m depth so that the organic matter can be converted to oil or gas. Reservoir rocks must be both porous and permeable, so that the petroleum liquids can be extracted, and should also take the form of a trap (e.g., an anticline) and capped with impermeable rock.
13. The optimum depth for the generation of oil from buried organic matter is 2,500 to 3,500 m.
14. Shale gas is an unconventional reserve because shale is not permeable enough to allow the gas to be extracted. The rock has to be fractured (fracked) to allow recovery. Fracking involves the use of vast amounts of water, and there is the potential that the fracking fluids can contaminate freshwater aquifers.
15. Kimberlite indicator minerals are much more abundant than diamonds within kimberlites, and so they can typically be detected further away from the kimberlite source, and over a much wider area.